全文获取类型
收费全文 | 179584篇 |
免费 | 860篇 |
国内免费 | 262篇 |
专业分类
化学 | 89652篇 |
晶体学 | 2635篇 |
力学 | 9377篇 |
综合类 | 7篇 |
数学 | 20911篇 |
物理学 | 58124篇 |
出版年
2020年 | 1848篇 |
2019年 | 2288篇 |
2018年 | 3395篇 |
2017年 | 3523篇 |
2016年 | 4157篇 |
2015年 | 1852篇 |
2014年 | 3586篇 |
2013年 | 7047篇 |
2012年 | 5533篇 |
2011年 | 6587篇 |
2010年 | 5510篇 |
2009年 | 5635篇 |
2008年 | 6360篇 |
2007年 | 6323篇 |
2006年 | 5617篇 |
2005年 | 4980篇 |
2004年 | 4821篇 |
2003年 | 4366篇 |
2002年 | 4521篇 |
2001年 | 4999篇 |
2000年 | 3691篇 |
1999年 | 2823篇 |
1998年 | 2603篇 |
1997年 | 2457篇 |
1996年 | 2253篇 |
1995年 | 2048篇 |
1994年 | 2005篇 |
1993年 | 2038篇 |
1992年 | 2073篇 |
1991年 | 2380篇 |
1990年 | 2314篇 |
1989年 | 2384篇 |
1988年 | 2264篇 |
1987年 | 2294篇 |
1986年 | 2125篇 |
1985年 | 2656篇 |
1984年 | 2670篇 |
1983年 | 2316篇 |
1982年 | 2371篇 |
1981年 | 2275篇 |
1980年 | 2076篇 |
1979年 | 2393篇 |
1978年 | 2547篇 |
1977年 | 2639篇 |
1976年 | 2729篇 |
1975年 | 2536篇 |
1974年 | 2467篇 |
1973年 | 2634篇 |
1972年 | 2152篇 |
1971年 | 1973篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
301.
The dependence of the type of magnetic ordering in multilayer structures on the magnitude of the exchange interaction between
the magnetic layers and on the degree of roughness of the interfaces between the layers is investigated. In the case of a
three-layer system the regions of existence of the domain structure, of noncollinear ordering of the homogeneous magnetic
layers, and of the collinear ferromagnetic phase and collinear antiferromagnetic phase are found.
Fiz. Tverd. Tela (St. Petersburg) 39, 1244–1247 (July 1997) 相似文献
302.
B. I. Sokil 《Ukrainian Mathematical Journal》1997,49(11):1777-1781
On the basis of periodic Ateb functions, in the resonance and nonresonance cases, we construct the asymptotic approximation of one-frequency solutions of a boundary-value problem for a nonlinear nonautonomous equation. 相似文献
303.
I. Nakai 《Commentarii Mathematici Helvetici》1998,73(2):177-205
A curvilinear d-web W = (F
1 , . . . , F
d
) is a configuration of d curvilinear foliations F
i
on a surface. When d = 3, Bott connections of the normal bundles of F
i
extend naturally to equal affine connection, which is called Chern connection. For 3 < d, this is the case if and only if the modulus of tangents to the leaves of F
i
at a point is constant. A d-web is associative if the modulus is constant and weakly associative if Chern connections of all 3-subwebs have equal curvature form. We give a geometric interpretation of the curvature form
in terms of fake billiard in §2, and prove that a weakly associative d-web is associative if Chern connections of triples of the members are non flat, and then the foliations are defined by members
of a pencil (projective linear family of dim 1) of 1-forms. This result completes the classification of weakly associative
4-webs initiated by Poincaré, Mayrhofer and Reidemeister for the flat case. In §4, we generalize the result for n + 2-webs of n-spaces.
Received: September 23, 1996 相似文献
304.
A highly selective solid phase extraction sorbent for pre-concentration of sameridine made by molecular imprinting 总被引:5,自引:0,他引:5
Summary A novel approach to solid phase extraction, based on the use of a highly selective molecularly imprinted polymer, is presented.
The versatility of this type of sorbent for solid phase extraction was demonstrated in a model batch-wise pre-concentration
of sameridine prior to gas chromatography. Problems associated with leakage of remaining imprint molecules during the desorption
phase could be eliminated by the use of a close structural analogue of sameridine as the imprint species. It was found that
a major benefit of the imprinted polymer was its specificity, which lead to distinctly cleaner chromatographic traces and
ability to improve sensitivity by extracting sameridine from larger sample volumes. 相似文献
305.
T. Engel M. Würtz S. Borneis St. Becker I. Klaft A. Kohl T. Kühl F. Laeri D. Marx K. Meier R. Neumann F. Schmitt P. Seelig L. Völker 《Hyperfine Interactions》1997,108(1-3):251-258
Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening
is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser
systems specialized on the specific needs of laser spectroscopy at storage rings is reported.
Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different
Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast
qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator.
It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a
frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz.
This laser can be advantageous for laser cooling of ion beams.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
306.
For fields above a critical value the expansion of the conductivity in powers of the field ceases to be valid and the weak-nonlinearity
approximation no longer works. The density behavior of the critical fields in strongly inhomogeneous media near the percolation
threshold is found on the basis of two criteria—an average criterion and a local criterion. The parameter values of the medium
for which crossover—a change of the critical behavior—occurs are determined. Similar calculations are performed for the critical
currents.
Zh. Tekh. Fiz. 68, 5–8 (June 1998) 相似文献
307.
The characterisation of iron-containing species in Chinkombe ilmenite and its reduction products was undertaken using Mössbauer Spectroscopic techniques. The ore was reduced by graphite in an inert atmosphere. The effects of such variables as quantity of reductant, temperature and preoxidation were investigated. The ore was completely reduced to alpha-iron and titanium dioxide with 20% carbon for a period of one hour at 1373 K. Chemical mechanisms are proposed for the reduction and oxidation of Chinkombe ilmenite. In the processing of ilmenite to obtain synthetic rutile, the ultimate desire is to separate the Fe phase from the TiO2. Mössbauer Spectroscopy has unambiguously confirmed the desired transformation of the iron phase according to thermodynamic predictions. The information gained would be used to choose the conditions of the reduction process. The alpha-iron could be separated physically or chemically from the completely reduced product mass to obtain synthetic titanium dioxide suitable for the paint industry. 相似文献
308.
V. I. Grafutin V. L. Grishkin G. G. Myasishcheva Yu. V. Funtikov Yu. A. Novikov 《Physics of the Solid State》1998,40(4):549-551
The empirical relation θ
p
6
/I
p=aK (where θ
p is the limiting angle of the parabolic component in the angular distributions of annihilation photons in metals, I
p is the integrated contribution of this component, K=1, 2, 3, ... is an integer, and a is a constant independent of the type of metal) observed earlier has been tested on magnesium, aluminum, copper, zinc, lead,
and bismuth samples. The validity of this relation has been substantiated. The value of the dimensionless constant a has been determined and was found to coincide within experimental error with the result obtained in previous measurements.
It is shown that the value of K for the same metal but for different samples may be different. It is conjectured that this may be due to different defect
concentrations in samples.
Fiz. Tverd. Tela (St. Petersburg) 40, 600–602 (April 1998) 相似文献
309.
The plane contact problem of steady thermoelasticity taking heat generation into account 总被引:2,自引:0,他引:2
The plane steady contact problem of thermoelasticity when there is heat generation from friction, which arises when an infinite cylindrical punch moves over the surface of an elastic half-space along its generatrix, is considered. It is assumed that heat exchange between the free boundary of the half-space and the surrounding medium obeys Newton's law, while the condition for ideal thermal contact exists in the region in which the solids interact. The problem is reduced to a system of three integral equations in the heat fluxes and temperature. The effect of the thermal and mechanical properties of the cylinder and the half-space on the main contact characteristics is investigated numerically. 相似文献
310.
Armenise I. Capitelli M. Colonna G. Koudriavtsev N. Smetanin V. 《Plasma Chemistry and Plasma Processing》1995,15(3):501-528
Plasma Chemistry and Plasma Processing - Nonequilibrium nitrogen dissociation-recombination kinetics in the boundary layer and on the surface of a solid body during hypersonic flow. the subsequent... 相似文献